San Francisco (CNN) -- Apple's Steve Jobs on Monday announced a new service called "iCloud," which lets Apple product owners store documents and music on the Internet instead of on their own computer hard drives or mobile phones.

iCloud expands on the trend of cloud computing, which refers to the idea that computer users are storing more of their information "in the cloud" of the Internet rather than on their own storage drives.

All of a person's Apple devices -- iPhone, iPads and Mac computers -- sync wirelessly with Apple's iCloud, giving users access to their documents, photos, apps, calendars and e-mails from any location, not just on a specific gadget.

"We think this is going to be pretty big," said Jobs, the co-founder of Apple, who has been on medical leave since January.

But the service does have some limits.

iCloud stores photos for up to 30 days, and mobile devices store the most recent 1,000 photos. Users can store only 5 gigabytes of documents, which is more than some competitors allow. And in order to sync music that wasn't purchased from Apple's iTunes store, users must pay Apple a fee of $25 per year.

"This is the first time we've seen this in the music industry," he said.

Consumers can use the iTunes portion of iCloud now, but only if they have iOS version 4.3. The rest of the features will be available to everyone in the fall.

The service replaces an old Apple product called MobileMe, which cost $99 per year. Daily back-ups on iCloud happen automatically in the background when a device is connected to the Internet over Wi-Fi, the company said.

Big tech players like Amazon and Google, as well as smaller companies like Dropbox, already operate cloud storage services with various features.

Apple typically uses its Worldwide Developers Conference or WWDC, as the event is called in tech circles, to announce a new version on the popular iPhone.

But not this year.

"If the hardware is the brain ... of our products, the software is their soul. And today, we are going to talk about software," Jobs said before a packed audience, wearing his standard uniform of a black mock turtleneck and jeans.

Analysts expect a new iPhone in September.

In addition to iCloud, the company on Monday announced new versions of its operating systems.

Mac OS X Lion, the company's new operating system for laptop and desktop computers, will be available next month for $30, the company said.

That operating system features new "gestures" that make computers work much more like tablets and touch-screen mobile phones.

"If anyone was doubting that iOS and OS X are converging, the use of the trackpad for gestures should convince you. It's incredibly tablet-like. But I wonder how much getting used to it'll take?" Gizmodo wrote on its live blog of the event, which started at 1 p.m. ET.

A new version of Apple's mobile operating system -- called iOS 5, which is due out in the fall -- introduces a system of alerts for iPhones and iPads. A "Notification Center" organizes alerts by app, and these alerts pop up at the top of the screen where they can be more easily ignored. Currently, these alerts show up in the center of the screen and interrupt users.

The mobile operating system also integrates with Twitter, allowing users to tweet photos from within the Camera and Maps apps.

"We want to make it easier for all of our customers to use Twitter," Apple's Scott Forstall said at the event in San Francisco.

A new built-in app called Reminders lets users create to-do lists, and an update to the iPhone and iPad e-mail system will let people create messages in bold or italics, as well as encrypt the messages they send from mobile devices.

The new mobile operating system will also debut a new app called iMessage. With it, iPhone, iPod Touch and iPad users will be able to send text, photo and video messages to each other without having to pay the cell-carrier fees associated with texting.

Research in Motion has a similar feature called BlackBerry Messenger, which is quite popular among owners of those phones. App developers have been selling similar software for iOS and other platforms, and those will likely continue to be popular because they allow, say, an iPhone user to contact an Android phone.

An update to the Camera app lets people take photos by pressing the volume-up button on the side of the iPad or iPhone.

The new Camera app also lets users edit photos on the fly, simulating features already available from many third-party app developers.

iOS updates will be available for the first time "over the air," meaning users won't have to sync their devices with desktop computers to get new software.